Center for Nuclear Receptor Signals, Hormone Research Center, School of Biological Science and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea.
Department of Integrative Medical Sciences, Northeast Ohio Medical University, Rootstown, Ohio 44272.
J Biol Chem. 2011 Dec 9;286(49):41972-41984. doi: 10.1074/jbc.M111.274514. Epub 2011 Oct 12.
Curcumin (diferuloylmethane), a major active component of turmeric (Curcuma longa), is a natural polyphenolic compound. Herein the effect of curcumin on endoplasmic reticulum (ER) stress responsive gene expression was investigated. We report that curcumin induces transcriptional corepressor small heterodimer partner-interacting leucine zipper protein (SMILE) gene expression through liver kinase B1 (LKB1)/adenosine monophosphate-activated kinase (AMPK) signaling pathway and represses ER stress-responsive gene transcription in an ER-bound transcription factor specific manner. cAMP responsive element-binding protein H (CREBH) and activating transcription factor 6 (ATF6) are both ER-bound bZIP family transcription factors that are activated upon ER stress. Of interest, we observed that both curcumin treatment and SMILE overexpression only represses CREBH-mediated transactivation of the target gene but not ATF6-mediated transactivation. Knockdown of endogenous SMILE significantly releases the inhibitory effect of curcumin on CREBH transactivation. Intrinsic repressive activity of SMILE is observed in the Gal4 fusion system, and the intrinsic repressive domain is mapped to the C terminus of SMILE spanning amino acid residues 203-269, corresponding to the basic region leucine zipper (bZIP) domain. In vivo interaction assay revealed that through its bZIP domain, SMILE interacts with CREBH and inhibits its transcriptional activity. Interestingly, we observed that SMILE does not interact with ATF6. Furthermore, competition between SMILE and the coactivator peroxisome proliferator-activated receptor α (PGC-1α) on CREBH transactivation has been demonstrated in vitro and in vivo. Finally, chromatin immunoprecipitation assays revealed that curcumin decreases the binding of PGC-1α and CREBH on target gene promoter in a SMILE-dependent manner. Overall, for the first time we suggest a novel phenomenon that the curcumin/LKB1/AMPK/SMILE/PGC1α pathway differentially regulates ER stress-mediated gene transcription.
姜黄素（二芳基甲烷），是姜黄（姜黄）的主要活性成分之一，是一种天然多酚化合物。本文研究了姜黄素对内质网（ER）应激反应基因表达的影响。我们报告姜黄素通过肝激酶 B1（LKB1）/腺苷单磷酸激活蛋白激酶（AMPK）信号通路诱导转录核心抑制子小异二聚体伴侣相互作用亮氨酸拉链蛋白（SMILE）基因表达，并以 ER 结合转录因子特异性方式抑制 ER 应激反应基因转录。cAMP 反应元件结合蛋白 H（CREBH）和激活转录因子 6（ATF6）均为 ER 结合 bZIP 家族转录因子，在 ER 应激时被激活。有趣的是，我们观察到姜黄素处理和 SMILE 过表达仅抑制 CREBH 介导的靶基因的反式激活，但不抑制 ATF6 介导的反式激活。内源性 SMILE 的敲低显著释放了姜黄素对 CREBH 反式激活的抑制作用。在 Gal4 融合系统中观察到 SMILE 的内在抑制活性，并且内在抑制结构域映射到 SMILE 的 C 末端，跨越氨基酸残基 203-269，对应于碱性区域亮氨酸拉链（bZIP）结构域。体内相互作用测定表明，SMILE 通过其 bZIP 结构域与 CREBH 相互作用并抑制其转录活性。有趣的是，我们观察到 SMILE 与 ATF6 不相互作用。此外，在体外和体内已经证明了 SMILE 和共激活因子过氧化物酶体增殖物激活受体α（PGC-1α）之间在 CREBH 反式激活上的竞争。最后，染色质免疫沉淀测定显示姜黄素以 SMILE 依赖的方式降低靶基因启动子上 PGC-1α 和 CREBH 的结合。总的来说，我们首次提出了一种新现象，即姜黄素/LKB1/AMPK/SMILE/PGC1α 通路差异调节 ER 应激介导的基因转录。
